I’m not acutely aware of the details of the sanctions, but I think time has shown that sanctions are no longer effective. The regime cares very little for its own population, and is very capable of repressing them to the extent that an insurrection isn’t likely.
What’s needed is some kind of agreement with China in order to disarm the DPRK (first resort). The current situation between the DPRK and China is unclear; whilst it’s possible that China has “lost control” of them, its also possible that China is using them as a geopolitical tool in their strategy against the US. A combination of the two is probably likely, but I doubt China really wants a nuclear armed DPRK.
The other option is unilateral military action against the DPRK in order to disarm them similar to Israel and Iran. This obviously has problems insofar that China could retaliate on their behalf, but it seems unlikely that China is going to start WW3 with the US (as long as the US doesn’t go into mission creep overload and attempt regime change); and also the threat of the North shelling the shit of Seoul and the rest of the ROK. I think this risk could be reduced if, as mentioned above, the strikes were limited in simply removing the DPRK’s nuclear capabilities and the threat of the North being annihilated by “fire and fury” if they retaliated against the South.
Any military action would need to be followed up with an enforced “deal” in order to maintain peace in the Korean peninsula, don’t ask me for details on that.
Ultimately it’s likely any kind of military action will result in civilian loss of life on both sides, as North Korea may figure they’ve got nothing left to lose with their nuclear capabilities removed. So I guess the question that needs to be asked is that potential loss of civilian life worth removing the risk of the North having a very real nuclear first strike capability? I personally think yes, but only once all the diplomatic options are excluded.